As disclosed in U.S. Pat. No. 4,146,688 (Schwindt et al.), it is known that aromatic diamines can be used as chain extenders in the preparation of polyurethanes. However, some aromatic diamines are too reactive with isocyanates to permit proper handling, and it has also been found that some aromatic diamines provide polyurethanes having unsatisfactory physical properties. Another problem apt to be presented by the use of aromatic diamines is that many such compounds are known to be toxic or have a structure such as to make it predictable that, when tested, they will probably prove to be carcinogenic.